This invention relates to continuous spinal anesthesia and particularly to an improved apparatus through which the anesthesia is administered.
Continuous spinal anesthesia has become a widely recognized technique in the last two decades, having been described by a variety of practitioners including Bizzari et al (Anesthesia and Analgesia 43: 393, 1964), Giuffrida et al (Anesthesia and Analgesia , 51: 117, 1972), and Shroff et al (Southern Medical Journal, 81 : 178 , 1988 ), among others. In the techniques described heretofore, generally a 17 to 21 gauge spinal needle was used to puncture the lumbar due at the desired interspace (L2-3 or L3-4) so as to enter the subarachnoid space, then a flexible catheter (about 20 gauge or 0.81 mm 0.D. to about 23 gauge or 0.56 mm 0.D.) reinforced with a metal stylet was inserted through the needle, the needle and stylet were withdrawn leaving the catheter in place, and anesthetic was administered through the catheter as required.
Continuous spinal anesthesia as described above has been recognized to provide a number of advantages over single dose injection including accurate control of the level and duration of anesthesia, induction of anesthesia with the patient in the operative position, the use of minimal doses of anesthetic, and the use of short acting anesthetics. In spite of these recognized advantages, however, the continuous technique has not been widely used by practitioners. One apparent reason for this lack of acceptance, among several postulated, is that the incidence of postdural puncture headache is sufficiently high to cause concern.
Postdural puncture headache is primarily attributable to the size of the needle used and incidence of headache decreases as the needle size decreases. Thus, the standard 25 or 26 gauge needle utilized in single injection spinal anesthesia produces a relatively low incidence of headache, while the larger 18 to 20 gauge needle required for continuous spinal anesthesia (the needle must be large enough to allow the catheter to pass through) produces a much greater incidence of headache. This disadvantage has thus prevented greater acceptance of the continuous spinal anesthesia technique.
In U.S. Pat. No. 3,780,733, an effort was made to overcome this disadvantage by coupling a thin 25 gauge needle to the end of a standard 20 gauge catheter and piercing the dura wall, so as to reach the subarachnoid space, only with this small gauge needle. To accomplish this, a larger 15 gauge needle was first partially inserted into the extradural space to act as a guide for the smaller catheter/needle unit. Then, the smaller catheter/needle unit was introduced through the lumen of the larger needle until it penetrated the subarachnoid space with assistance from a stylet inserted in the catheter.
While presumably the apparatus and technique disclosed in the above described patent would achieve a reduction in the incidence of postdural puncture headache, it is believed that the apparatus contemplated would be difficult to manufacture and would raise additional concerns that would detract from its use. One such concern would be the permanence of the coupling connecting the small needle to the catheter. If the needle could be accidentally dislodged while in the patient, the result could be disastrous. A second concern would be the maintenance of a sharp metal needle in the subarachnoid space during surgery. Any unnecessary movement of the needle could cause damage beyond the initial puncture. Neither of these concerns is present if only a flexible, one piece polymeric catheter is inserted in the subarachnoid space.